The right hemisphere's role in action word processing: a double case study.

Word category-specific deficits were investigated in two patients with right hemispheric lesions and hemiparesis affecting the left extremities. Words from three categories, action verbs, nouns with strong visual associations and nouns with both strong action and visual associations, were presented in a lexical decision task. The stimulus categories were matched for word length and frequency. In both patients, responses to action verbs were slowed and/or less accurate compared with the other word categories. This was so even in the patient with a minor lesion in the motor, pre-motor and somatosensory areas of the hand representation. Control subjects did not show category differences when tested with the same stimulus materials. These results are consistent with the view that the cortical areas involved in the programming of body movements, even those in the hemisphere not dominant for language, specifically contribute to and are necessary for the processing of words referring to such movements. As an alternative, the affected brain areas may be of particular relevance for the processing of words from the lexical category of verbs. The results are consistent with a brain model of language based on Hebb's cell assembly concept.